Methods and apparatus for drying an grinding moist feed materials are known in many different forms, such as can be seen for example from W. H. Duda, CEMENT-DATA-BOOK, Volume 1, third edition, 1985, for instance pages 235 to 241. Roll mills typically used for this drying and grinding are constructed with a mill housing having a substantially vertical axis. In this mill housing a mill part (grinding part) is disposed in the lower part for the material comminution and an air separator is disposed in the upper part. The mill part contains a drivable and rotatable grinding table and a plurality of grinding rolls which roll thereon. Moist fresh feed material is delivered to the grinding table approximately in the centre, so that it is comminuted between the upper grinding surface of the grinding table and the grinding rolls. At least a proportion of the comminuted mill feed material is conveyed into the separator by a rising stream of hot gas delivered to the mill part, and is thereby dried. Sufficiently comminuted fine material is drawn off together with the hot gas stream from the air separator, whilst oversize material which is not yet sufficiently comminuted, so-called tailings, is returned to the grinding table in order to be further comminuted there.
In the practical use of the known methods and roll mills, difficulties always occur with the delivery of the moist feed material, involving amongst other things an unwanted incrustation of the fresh feed material in the region of the delivery arrangement.
The object of the invention is to provide an improved method and apparatus wherein by relatively simple means, even with relatively moist fresh feed material, it is always possible to ensure a reliable delivery of fresh material to the grinding table of the mill part.